The River Thames ( (listen) TEMZ), known alternatively in parts as the River Isis, is a river that flows through southern England, including London. At 215 mi (346 km), it is the longest river entirely in England and the second-longest in the United Kingdom, after the River Severn.

The river rises at Thames Head in Gloucestershire, and flows into the North Sea near Tilbury, Essex and Gravesend, Kent, via the Thames Estuary. From the west it flows through Oxford (where it is sometimes called the Isis), Reading, Henley-on-Thames and Windsor. The Thames also drains the whole of Greater London.The lower reaches of the river are called the Tideway, derived from its long tidal reach up to Teddington Lock. Its tidal section includes most of its London stretch and has a rise and fall of 23 ft (7 m). From Oxford to the Estuary the Thames drops by 55 metres. Running through some of the drier parts of mainland Britain and heavily abstracted for drinking water, the Thames' discharge is low considering its length and breadth: the Severn has a discharge almost twice as large on average despite having a smaller drainage basin. In Scotland, the Tay achieves more than double the Thames' average discharge from a drainage basin that is 60% smaller.

Along its course are 45 navigation locks with accompanying weirs. Its catchment area covers a large part of south-eastern and a small part of western England; the river is fed by at least 50 named tributaries. The river contains over 80 islands. With its waters varying from freshwater to almost seawater, the Thames supports a variety of wildlife and has a number of adjoining Sites of Special Scientific Interest, with the largest being in the North Kent Marshes and covering 5,289 ha (20.4 sq mi).

The Boat Race is an annual set of rowing races between the Cambridge University Boat Club and the Oxford University Boat Club, traditionally rowed between open-weight eights on the River Thames in London, England. There are separate men's and women's races, as well as races for reserve crews. It is also known as the University Boat Race and the Oxford and Cambridge Boat Race. The men's race was first held in 1829 and has been held annually since 1856, except during the First and Second World Wars (although unofficial races were conducted) and the COVID-19 pandemic in 2020. The first women's event was in 1927 and the race has been held annually since 1964. Since 2015, the women's race has taken place on the same day and course, and since 2018 the combined event of the two races has been referred to as "The Boat Race".

The Championship Course has hosted the vast majority of the races. It covers a 4.2-mile (6.8 km) stretch of the Thames in West London, from Putney to Mortlake. Other locations have been used, including a stretch of the River Great Ouse which was the venue for the 2021 race. Members of both crews are traditionally known as blues and each boat as a "Blue Boat", with Cambridge in light blue and Oxford in dark blue. As of 2021, Cambridge has won the men's race 85 times and Oxford 80 times, with one dead heat, and has led Oxford in cumulative wins since 1930. In the women's race, Cambridge have won the race 45 times and Oxford 30 times, and has led Oxford in cumulative wins since 1966. A reserve boat race has been held since 1965 for the men and since 1966 for the women.

In most years over 250,000 people watch the race from the banks of the river. In 2009, a record 270,000 people watched the race live. A further 15 million or more watch it on television.